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Home >> GMC >> 1998 >> Forward Control 6.5 F >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System - Tests W/Codes - Introduction >> Self-Diagnostic System >> On-Board Diagnostic (OBD) System Check >> 4.6L

On-Board Diagnostic (OBD) System Check: 4.6L

  1. Check if MIL is illuminated with engine running. Check for driveability concerns, or faulty computer-controlled components. If a problem is found, go to next step. If no problems are found, system is okay.
  2. Ensure battery is fully charged. Turn ignition off. Connect scan tool. Turn ignition on. If scan tool displays PCM data, go to next step. If scan tool does not display PCM data, go to DLC DIAGNOSIS OR NO SCAN TOOL DATA .
  3. Attempt to start engine. If engine starts and continues to run, go to next step. If engine does not start, or starts and stalls, go to NO START DIAGNOSIS in appropriate BASIC DIAGNOSTIC PROCEDURES article.
  4. Using scan tool, observe DTC status for MIL REQUEST, FAIL THIS IGN, LAST TEST FAIL and HISTORY. If any DTCs are present, diagnose DTCs. See DIAGNOSTIC TESTS in appropriate TESTS W/CODES article. If no DTCs are present, go to next step.
  5. Compare scan tool engine data with typical control system data values. If data values are within limits, see appropriate TROUBLE SHOOTING - NO CODES article. If data values are not within limits, see appropriate SYSTEM & COMPONENT TESTING article.
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